I definately wouldnt add corals for a while. Probably a couple months. Looks pretty good so far man, is that a 20 high instead of a 20 long? Slime algae are actually cyanobacteria and are a normal part of the cycle. You can add critters that like to eat it (hermit crabs, baby conch, or Chevron and Mimic tangs) or you can find a tank that is balanced and slime algae free and inoculate your tank with a few teaspoonsful of substrate. There are other microorganisms that eat the algae that can help you out.
You can also reduce the light cycle, or if there is nothing light sensitive in the tank, leave it in darkness for a couple of weeks. The algae cant grow without light and you dont need lights to cycle your tank.